1. Field of the Invention
This invention relates to an illuminating light source device using a semiconductor laser which is most suitable for an illuminating light source installed at a vibrating place in a vehicle or tunnel or a portion where an electric lamp is hardly exchangeable for new one, as well as for general luminairs such as room and street lamps and a flash light.
2. Description of the Prior Art
A light source generally for use in illumination includes an incandescent lamp, which can obtain visible light through the heat radiation from an incandesced filament caused by applying current to the filament in a vacuum glass bulb charged with argon gas or the like, and a fluorescent lamp which can convert ultraviolet rays (wavelength of 253.7 nm) resulting from the impaction of thermoelectrons from an electrode filament in a low pressure glass tube of a pressure of about 1 Pa (6 to 10.times.10.sup.-3 Torr) charged with mercury vapor of a pressure of 1000 Pa (2 to 3 Torr) against mercury atoms, into visible light by irradiating the resultant ultraviolet rays to a fluophor applied to the inside surface of a fluorescent tube.
In addition, the light source described above includes a light emitting diode (which will be referred to as LED thereafter) as a display element used in OA (Office Automation) apparatuses and display units. The LED is adapted to emit light by applying current to p-n junction of a semiconductor. A various kinds of LEDs have been put to practical use and manufactured to be in wide use in the range from infrared rays for use in remote-controlled sensors and optical communication systems to visible light or use in displays by properly selecting the kind and composition of crystal.
A visible radiation LED includes a LED having a luminescent layer such as GaAlAs (660 nm: red), GaAsP (N dope) (590 nm: yellow), GaP (555 nm: green), SiC (470 nm: blue) and GaN (450 nm: blue). A visible radiation LED having high luminance available from red to less-developed blue has been obtained at low cost.
However, the incandescent lamp involves the following problems. Namely, since the current is nearly lost as heat and part of the current is radiated as light, the incandescent lamp is inferior in luminous power conversion efficiency. In addition, the incandescent lamp has large power consumption, and is weak in vibrations or the like and inferior in durability (average service life of a usual illuminating lamp is about 1000 hours.).
On the other hand, although the fluorescent lamp generates nearly no heat in comparison with the incandescent lamp and has satisfactory luminous power conversion efficiency, it still involves the following problems. Namely, the fluorescent lamp has large power consumption and is inferior in durability (the average service life is about 10000 hours). In addition, the fluorescent lamp is difficult to be miniaturized.
Further, the LEDs having various colors have been put into practical use as the visible radiation LED which is advantageously inexpensive and has small power consumption. However, the visible radiation LED generates weak radiant power output and is difficult to be adapted for illumination.
Incidentally, a portable illuminating device such as a flash light and a search light has been proposed as an illuminating light source device using a semiconductor laser (e.g., Japanese Utility Model Laid-open No. 4-16801 or the like). The portable illuminating device uses a visible radiation semiconductor laser as a light source and is adapted to obtain a divergent luminous flux by diffusing visible light from the semiconductor laser through a concave diffusion lens. However, since the semiconductor laser outputs coherent monochromatic light and cannot obtain white light for use in illumination differently from the case of the incandescent lamp and the fluorescent lamp, it involves a problem in that only red or green monochromatic light can be obtained by the semiconductor laser. Further, the semiconductor laser for red or green monochromatic light generates insufficient radiant power output for the present time, and cannot be utilized for illumination as it is.